The invention relates to an anti-locking control system for preventing locking of the wheels of a vehicle during braking. WO 88/06544, to which U.S. Ser. No. 392,932 corresponds, described a system having wheel speed sensors which generate signals corresponding to the speeds of the respective wheels, an evaluation circuit which processes these signals into brake pressure control signals, and brake pressure control devices to which the control signals are fed to prevent locking. There, the vehicle deceleration is ascertained from the slope of an auxiliary reference. During a rapid drop of wheel speeds, the ascertained slope determines the progression of the reference signal needed to determine slip.